Field
Embodiments relate to glass compositions and in particular, to glass compositions useful for thin film photovoltaic (PV) modules.
Technical Background
The fusion forming process typically produces flat glass with optimal surface and geometric characteristics useful for many electronics applications, for instance, substrates used in electronics applications, for example, display glass for LCD televisions, where the high quality of the surface is necessary to specialty glasses for photovoltaics modules.
Photovoltaic modules are used to convert sunlight into electricity. Two major types used or in development today are wafered modules using multiple silicon wafers connected together and thin film modules using one of a variety of inorganic then film materials, such as cadmium telluride (CdTe), copper indium gallium di-selenide (CIGS) or thin film (amorphous and microcrystalline) silicon. Typical packages for the thin film modules have a glass substrate, such as a soda lime glass, back contact, the semiconductor layer or layers, such as CIGS, a front transparent contact layer (TCO) and a protective cover layer, such as a glass substrate. The modules may further have edge seals, a metal frame, and electrical contacts.
There is a continuing drive to make PV technology competitive with existing power production methods, e.g., hydro, coal, nuclear, wind, etc., in the power generation industry. To do so, manufacturing costs, conversion efficiency, and efficiency degradation are some of the design challenges that need to be addressed. Soda lime glass has been a common substrate for CIGS because of its low cost and the fact that it contains sodium, which has been shown to yield a substantial open-circuit voltage increase in CIGS PV devices. However, soda lime glasses are not ideal for PV modules—the sodium delivery can be difficult to control, occur too quickly or in amounts too large. Further, soda lime glasses can have sodium release issues that occur due to environmental conditions. As soda lime glass ages in ambient conditions of temperature and humidity, its surface chemistry changes in a manner that results in a spatially non-uniform release of sodium during CIGS thin film deposition. These problems can lead to delamination issues and reduced efficiency. Clearly, there is still an unmet need to find glass compositions that provide optimal substrates for thin film PV devices.